Earth’s Oceans Part 2: Properties of Ocean Water
Composition • Ocean water is a mixture of gases and solids dissolved in pure water. • 96.5% H2O • 3.5% or 35 0/00 (parts per thousand) dissolved salts • Most of the 90 naturally occurring elements have been found in seawater Image credit: HannesGrobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Salts in Ocean Water • Salinity – the amount of dissolved salts in water • # of grams of dissolved salts in 1 kg of water = parts per thousand (0/00) • Average for ocean water is 35 0/00 • Range is ~33-37 0/00 • If the mass of all the oceans combined is about 1.4 × 1021kg, how much salt is there dissolved in all? • 1.4 × 1021kg x .035 kg/kg = 4.9 x 1018kg of salt = 4,900,000,000,000,000,000 = 4.9 billion billion kg FYI: This is enough salt to cover all the Earth’s land surface with a layer of salt 500 ft. thick.
Salts in the Ocean Video: http://www.youtube.com/watch?v=aFXn1d5baCo Sources of Salts • Weathering and erosion of rock of the Earth’s crust, including wave action • Dissolving of salts by rains and running water that carry them to the sea • Volcanic activity in oceans (gases and solids that escape from vents) Credit: NSF and NOAA
Salts in Ocean Water • Note lower salinity to the north of the Amazon River • Most of very high or low readings right at coastlines are due to satellite signal distortion http://earthobservatory.nasa.gov/IOTD/view.php?id=78250&src=flickr
Salts in the Oceans • Various factors affect salinity at a given location. Examples: • Near the Amazon, Mississippi, and Congo River basins salinity is lower due to large influx of fresh water • High rates of evaporation in tropical regions, such as the Red Sea area, causes higher salinity • Freezing of water into ice in the polar regions increases salinity as the salts are left behind in the liquid water • Living organisms reduce the amount of calcium salts from what would be otherwise expected as they use them to make their shells
Gases in Ocean Water • Most abundant are nitrogen, oxygen, argon, and carbon dioxide. • Highest amounts are near the ocean’s surface, where these gases are exchanged with the atmosphere. • Oxygen and carbon dioxide are necessary for respiration and photosynthesis respectively. • Much of the carbon dioxide converts into carbonic acid or bicarbonate • Bicarbonate, as calcium bicarbonate, is needed to by organisms to form shells
Gases in Ocean Water Factors that affect the amount of gas dissolved: • Temperature of the water - cold water holds more gas than warm water • Salinity – low salinity water can hold more gas than high salinity water • Depth – as depth increases pressure increases and more gas can be dissolved • Amount of living organisms in the water– water with a lot of photosynthesizing organisms will be oxygen-rich • Oxygen is carried to deep waters when the water cools, as in polar areas, or becomes more saline (both cause an increase in density).
Temperature of Ocean Water Surface Zone: • Sun warms the surface. • Heat is transferred downward by the mixing action of waves and currents • Extends 100 to 400 meters deep and temperature remains fairly constant through the zone • Temperature varies with location and season
Temperature of Ocean Water Thermocline: • Temperature drops off rapidly • Depth of thermocline varies depending on season and the flow of currents • Occurs because warm surface water and cold deep water do not easily mix Graph showing a tropical ocean thermocline (depth vs. temperature). Note the rapid change between 100 and 200 meters.
Temperature of Ocean Water Deep Zone: • Extends from the bottom of the thermocline to depths of 4,000 m or more • Temperature decreases only slightly • Below 1,500 m the temperature is about 4°C • In the polar oceans the three zones do not exist as even the surface waters are very cold. • Video: http://oceantoday.noaa.gov/takingtheoceanstemp/